The ongoing aim of this project is to develop a novel, computer- based technique that can be used to delineate, in the human, the neural control and biomechanical mechanisms associated with complex lower extremity motor tasks. Eventually, it is our goal to be able to use this technique to specify the motor coordination strategies that the human central nervous system ought to employ to stand and walk, first in able-bodied persons and later in neurologically- or musculoskeletally-disabled persons. Another goal is to use this technique to assist in the design of patient- specific rehabilitation strategies. Once developed, therefore, this technique may well lead to improved methods of neurological and physical rehabilitation. The computer technique under development is based on optimal control theory, which is highly-developed framework for analysis of complex dynamical systems. However, this theory requires a mathematical formulation of the task to be optimized. One major problem associated with the few previous attempts employing this theory is that the performance criterion cannot be specified with certainty. Our study of maximum jumps and pedaling at high effort circumvents this problem and has let us focus on the development of a mathematical, computer-implemented representation of musculotendon dynamics and musculoskeletal geometry. This representation is needed for computer studies of jumping and pedaling, as well as any motor task involving the lower extremities. The goals are, by using jumping and pedaling as examples of complex motor tasks, to conduct computer studies and experiments: 1. to comprehend how intermuscular coordination, inertial coupling among body segments, musculotendinoskeletal dynamics, and energetics interact to produce synergistic movement; and 2. to understand how muscle strength and speed, elasticity in tendon and muscle, and kinematic constraints affect human coordination and energetics. In contrast to experimental data alone, it is hypothesized that our computer studies will augment one's ability to understand complex movement, such as how and to what degree muscles need to be coordinated, and how limb structure and biomechanical constraints affect coordination.